GMAT Prep ques:

[thumpin_termis]

I just went through the GMATPrep exam, and there were 2 DS questions which I had no idea how to go about it. Can someone help me out?

Thanks in advance!

[jayhawk2001]

Problem 1:

P(white or even) = P(white) + P(even) - P(white & even)

1 - insufficient. We don't know P(white) and P(even)

2 - insufficient. We don't know P(white & even)

1 & 2 insufficient. We just know P(white) - P(even). We can't find out
P(white) + P(even)

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Problem 2:

1 - insufficient. Take x=30, y=50 and x=70,y=50. We can get
multiple values for xy. No unique soln.

2 - insufficient. LCM=180. Can be x=45, y=4 or x=9,y=20. No
unique value

1 & 2 together sufficient.

180 = 10 * 2 * 3 * 3

We know 10 has to be a factor of both numbers. We also know that 3
cannot be a factor of both numbers (else the greatest common factor
will be 90, not 10).

So, only possible way to split this is 10*2, 10*3*3 i.e. 20,90 or 90,20
both of which yield the same value for xy.